Add reusable staking attestation test workflow

Support TropiBot dispatch fallbacks in staking tests

Adds a new optional 'ipfs_hash' input to staking-sync-test and
staking-attestation-test. When the wrapper passes a pre-built IPFS hash
(via repository_dispatch client_payload or workflow_dispatch input), the
test job prefers it over the freshly built hash from the build job. When
no input is provided, behavior is unchanged: the build job still runs and
its hash is used.

The build job is intentionally kept always-on for now; this is purely
forward-looking plumbing so the wrappers can forward the dispatch
payload's ipfs_hash. A future change can short-circuit the build job
when an input hash is present.

ci: add optional ipfs_hash input to staker test reusable workflows

Provides a single reusable workflow that runs
`npx @dappnode/dappnodesdk github-action build` on every push and PR,
pins the result to IPFS via Pinata, and posts a comment with the install
link on the triggering PR. Replaces the duplicated build.yml stubs
currently living in each DAppNode package repo.

Inputs:
- all_variants (bool): build all package variants
- variants (string): comma-separated variant list

Required secrets (passed via `secrets: inherit`):
- PINATA_API_KEY
- PINATA_SECRET_API_KEY

ci: add dappnode-build-hash reusable workflow

The SDK uses whatever GITHUB_TOKEN is passed in to author the PR
comment. With the default workflow token the comment is posted as
`github-actions`. Switch to a tropibot App installation token (the
same one used by bump-upstream, staking-release, etc.) so the comment
is posted as `tropibot[bot]`, matching the rest of the build-action
comments in the dappnode org.

Pattern mirrors `bump-upstream.yml`: `actions/create-github-app-token@v3`
mints a per-run token from `vars.TROPI_APP_ID` + `secrets.TROPI_APP_PRIVATE_KEY`.
Both flow automatically to callers via `secrets: inherit` / `vars` context.

ci: post IPFS hash comment as tropibot[bot]

Aligns with the other reusable workflows in this repo (staking-release,
staking-sync-test, staking-attestation-test).